LONDON: People who stop using weight-loss injections such as Wegovy and Mounjaro regain weight up to four times faster than those who stop conventional dieting and exercise, according to new research published in the British Medical Journal (BMJ).
The study found that while patients using injectable weight-loss drugs lost substantial weight — around 20 per cent of their body weight on average — they regained about 0.8 kilograms per month after stopping treatment.
At that pace, most returned to their pre-treatment weight within about 18 months.
By contrast, people who relied on dieting and exercise alone regained weight more slowly, at roughly 0.1 kilograms per month, although results varied between individuals, researchers said.
Findings from clinical trials
The research examined data from 37 studies involving more than 9,000 participants. Only eight studies assessed newer GLP-1 drugs such as Wegovy and Mounjaro.
The longest follow-up period after stopping medication was one year, meaning the estimates are based on limited long-term data.
“People buying these need to be aware of the risk of fast weight regain when the treatment ends,” said lead investigator Dr Susan Jebb of Oxford University.
She cautioned that the findings were drawn from clinical trials rather than real-world use and said longer studies were needed to understand the long-term effects of the drugs.
Why weight returns quickly
GLP-1 drugs mimic a natural hormone that regulates appetite. Dr Adam Collins, a nutrition expert at the University of Surrey, said the way the drugs affect the brain and body may explain rapid weight regain.
“Artificially providing GLP-1 levels several times higher than normal over a long period may reduce the body’s own GLP-1 production and sensitivity,” he said.
“When the drug is withdrawn, appetite is no longer kept in check and overeating becomes much more likely.”
He added that stopping treatment suddenly was especially challenging for people who had not made lasting dietary or behavioural changes.
Guidance and long-term use
Some people who stopped taking the injections described a sudden return of intense hunger.
“One woman said it felt like a switch had been flipped and she was instantly starving,” the report noted, adding that patients described strong urges to eat after coming off the drugs.
The UK’s National Health Service recommends weight-loss injections only for people who are overweight and have obesity-related health risks.
Doctors are also advised to prescribe lifestyle changes, including healthier diets and regular exercise, to help patients maintain weight loss.
Many clinicians now consider the drugs a long-term or even lifelong treatment due to the high risk of relapse after stopping.
Currently, there is no fixed time limit for NHS prescriptions of Mounjaro, while Wegovy can be prescribed for a maximum of two years.
General practitioners cannot automatically continue prescriptions initiated privately unless patients meet NHS eligibility criteria.
Growing use of “skinny jabs”
Researchers from University College London estimate that about 1.6 million UK adults used weight-loss injections in the past year, mostly through private prescriptions.
A further 3.3 million people say they would like to use the drugs in the coming year.
That means around one in 10 UK adults has either used or is considering using the injections, based on nationally representative surveys conducted in early 2025 and funded by Cancer Research UK.
Use was twice as common among women as men and highest among people aged in their 40s and 50s.
Obesity as chronic condition
Professor Naveed Sattar of the University of Glasgow said the drugs could offer important health benefits by reducing weight quickly.
“It’s plausible that being lighter for even two to three years could slow damage to joints, the heart or kidneys,” he said, adding that longer trials were needed to confirm such benefits.
He noted that continued use over three to four years allowed patients to maintain significantly lower weight — a result rarely seen with lifestyle-only approaches.
A spokeswoman for Eli Lilly, which manufactures Mounjaro, said weight-loss drugs should be used alongside healthy eating, physical activity and medical supervision.
“When treatment is stopped, weight can return, reflecting the biology of obesity rather than a lack of effort,” she said.
Novo Nordisk, the maker of Wegovy, said the findings highlighted obesity as a chronic condition requiring ongoing treatment, similar to diabetes or hypertension, to sustain health benefits.
